Identification of a functional <scp><i>DOCK8</i></scp> gene polymorphism associated with atopic dermatitis
Authors: Kazufumi Kunimura, Kazuhiko Yamamura, Takeshi Nakahara, Makiko Kido‐Nakahara, Takehito Uruno, Yoshinori Fukui
Journal: Allergy (2022)

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by recurrent eczematous lesions, intense itch, and type 2 immune responses. Interleukin 31 (IL-31) is a cytokine mainly produced from skin-homing CLA+ T cells.1, 2 Serum IL-31 levels correlate with the disease severity of AD patients,2 and the administration of an anti-IL-31 receptor antibody alleviates pruritus in AD patients.3 Thus, IL-31 plays a major role in AD pathogenesis. Dedicator of cytokinesis 8 (DOCK8) is an evolutionarily conserved guanine nucleotide exchange factor (GEF) for Cdc42.4 Bi-allelic loss-of-function mutations of DOCK8 cause a combined immunodeficiency characterized by AD.5 We have previously shown that knock down of DOCK8 gene in T cells from healthy controls markedly increases T-cell receptor-mediated IL31 gene expression.6 Therefore, DOCK8 acts as a negative regulator for IL-31 induction in human T cells. However, DOCK8 expression is comparable between healthy controls and AD patients,6 and functional significance of DOCK8 in the disease predisposition remains unknown. The aim of this study was to evaluate whether DOCK8 gene polymorphism is associated with AD. We recruited age- and gender-matched 46 AD patients and 46 healthy controls (Table S1). Blood samples were obtained from all participants according to the institutional review board approvals. Gene polymorphisms in all exons of DOCK8 (Exon 1–48) were analyzed by direct DNA sequencing using exon-specific primers (Table S2). The difference of allele and genotype frequencies between patients and control samples was compared using the chi-square test. Among the sequences of all the 48 DOCK8 exons, only the frequency of the DOCK8 allele encoding T instead of C at position 1790 (DOCK8 + 1790 T allele, rs17673268) showed significantly higher frequency in AD patients than that in the controls (Table 1, 50% vs. 34%; odds ratio [OR] = 1.96; p = .025). In addition, the frequency of the TT genotype significantly increased in AD patients (Table 1), suggesting that this genotype contributes to disease susceptibility to AD. Moreover, severe AD (Investigator Global Assessment [IGA] score: 4) was observed only in patients with CT and TT genotypes (Figure S1). When AD patients were subdivided into two populations with IGA scores of 4 or ≤3, the frequency of the TT genotype significantly increased in patients with IGA scores of 4, compared with patients with IGA scores of ≤3 (p = .029; Table S3). We made further comparisons of EASI scores between CT and TT genotypes in moderate-to-severe patients, which indicate that EASI scores were significantly higher in patients with TT genotype than those with CT genotype (p = .005; Figure S2). We previously identified endothelial PAS domain protein 1 (EPAS1) as a master transcriptional factor essential for T-cell receptor-mediated IL-31 induction.6 Although EPAS1 translocates to the nucleus in response to hypoxia to mediate promoter activation of target genes, this process is negatively regulated by DOCK8, independent of its Cdc42 GEF activity.6 To better understand whether DOCK8 + 1790 T allele affects EPAS1 nuclear localization, the fluorescence intensity of intranuclear EPAS1 was analyzed after stably expressing DOCK8 + 1790C allele or + 1790 T allele (NM_203447.3:c.1790C > T; p.Ala597Val) in the human cell line HCT116 lacking endogenous DOCK8 protein (Figure S3). When +1790C allele was expressed in HCT116 cells, hypoxia-induced nuclear translocation of EPAS1 was inhibited (Figure 1). However, such inhibitory effect was not seen for +1790 T allele (Figure 1). Collectively, these results indicates that the TT genotype of DOCK8 gene augments IL-31 production by promoting EPAS1 nuclear localization. In conclusion, we found that DOCK8 polymorphism at position 1790 (rs17673268) is associated with the susceptibility to AD and revealed its underlying molecular basis. Although this study used a relatively small sample size, our findings provide a novel insight into AD pathogenesis. The authors acknowledge technical assistance from Arisa Aosaka, Sawako Sakai, and members of the Laboratory for Research Support of the Medical Institute of Bioregulation in Kyushu University. We thank Chie Kikutake in the Medical Institute of Bioregulation in Kyushu University for statistical consulting. We also thank all study subjects for participation in this study. This project was supported by Medical Research Center Initiative for High Depth Omics. This work was supported by Japan Agency for Medical Research and Development (AMED) under grant number JP19gm0010001, JP20ek0410064, and JP21gm1310005 (to Y.F.). The authors declare that they have no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request. AppendixS1 Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.